I. Field of the Invention
This invention relates to the field of gas monitoring. The invention provides a method and apparatus for wireless monitoring of gases, including toxic and combustible gases, with a device that has a radio transmitter that transmits quantitative gas levels to a master controller or multiple master controllers.
II. Description of the Related Art
Toxic gas monitoring systems are well known. Generally, gas monitors are placed around chemical producing facilities such as a chemical processing plant. These monitoring systems are configured to monitor for the presence of toxic and/or combustible chemicals. In addition to monitoring for the presence these chemicals, typically in parts per million or lower explosive limits, these detectors can also detect other important information such as wind speed and direction, temperature and other weather conditions. This information is then relayed to some sort of output system. For instance, the information can be relayed back to the control center of a chemical plant and be displayed on a computer terminal or be comprised in a computer printout.
Conventional toxic gas monitoring systems comprise multiple sensing units. These units are placed around the perimeter of a chemical processing plant, for example, to constantly monitor the conditions around the plant. Upon detection of a toxic gas, usually at a predetermined level, the unit may sound an alarm in addition to relaying the information to the control center. This information can be used, for example, to determine the source of the gas so that an unexpected leak can be corrected. Alternatively, should the plant simply be operating at too high of a capacity and thus be generating too much toxic waste, its operations can be brought to within acceptable tolerances. Additionally, the wind speed, weather conditions and direction of the gas can be used to determine which people need to be warned about the presence of toxic gas and when such a warning should be issued.
Typically, in gas detection systems a master site provides information to a computer. U.S. Pat. Nos. 5,553,094, 5,568,121 and 5,771,004 disclose such systems. U.S. Pat. No. 5,597,534 discloses a circuit that measures a chemical sensor output. Typically, specially designed software is incorporated as well. For example, the Gastronics' Event Scada Software is an unlimited tag Scada software which runs off Windows '95 or Windows NT and is designed for user friendliness along with the ability to customize and map out the geography of a plant. The Event Scada Software offers the user the flexibility to design and customize individual screens to match different applications. An assortment of tools allows the creation of trend charts, wind speed and direction, alarm settings and maintenance screens. A multilevel security feature may be included to prevent unauthorized access to customization functions.
Currently, the method of relaying this important information from the monitors to the control center has been through wires which physically connect each of the monitors to the output system. This is generally referred to as "hard wiring." Hard wiring requires each monitor to be physically connected to the output system by some sort of wire or cable. Hard wiring each of the numerous monitors to the control system can be quite costly, cumbersome and require substantial and frequent maintenance. For example, should the output system ever need to be relocated, such as in a different control room or outside of the plant, the cables would need to be rerouted to this new site. Rerouting all of the cables is labor intensive and expensive.
To further complicate matters, the wires may need to be buried in the ground (typically below the frost line) to comply with building code requirements or simply as a precautionary measure. Burying multiple wires in the ground requires substantial excavation which is rarely inexpensive. Similarly, repairing, replacing or moving these wires also requires substantial, expensive excavation.
Alternatively, the wires may need to be suspended at a height substantially above ground level. Such suspension may require the installation and maintenance of some sort of suspension devices, such as telephone poles. These poles would be placed in and around the chemical plant. This, again, may be an expensive undertaking. Finally, with regard to hard wiring, the wires themselves are usually expensive and are prone to breaking, cracking or failing in some sort of way. Thus, it is apparent that a wireless toxic gas monitoring system is desirable. The present invention comprises such a wireless toxic gas monitoring system.
It is common to monitor gas levels around large plants. Additionally, it is not uncommon for gas monitors to be placed some distance from these large plants. Consequently, the monitors may have to transmit information a substantial distance. Moreover, because the destination of this information is often located somewhere deep within the plant, e.g., a central control room, the monitors may need to relay this information through physical objects, such as layers of concrete, steel, insulation and other building materials.
In addition to physical barriers, the monitors usually need to transmit the information through substantial interference as well. Electric equipment and communication systems existing in almost all plants create vast amounts of interference such as electromagnetic waves, for example. Thus, a wireless gas monitoring system that is able to transmit information over a substantial distance and through substantial amounts of interference is desirable. The current invention utilizes, but is not necessarily limited to, licensed radio frequencies that operate at higher powers and are therefore able to transmit over large distances and through substantial amounts of interference.
Radio telemetry has recently been used as a lower cost alternative to hard wiring the monitors to the output or control systems. However, currently such radio telemetry has been limited by technology such that each monitor must have its own radio and remote terminal unit (RTU). A typical radio telemetry system using RTU's, while reducing significant installation costs, still requires both the high cost of the RTU as well as the installation costs to wire the gas monitors to the RTU. With the advent of the current invention, the advantages of wireless toxic gas monitoring systems are realized. This is particularly true with respect to very long conduit runs, such as with perimeter monitoring applications, where the cost of the RTU and wiring the sensors to the RTU is increased by the long lengths of conduit and installation costs.
Additionally, most monitors of the related art are event triggered only. By this it is meant that the monitors only relay a signal when they detect a high level of gas. The monitors merely let you know when a threshold level of gas (such as a gas denoted "alpha") has been surpassed. For instance, if a system were set to detect 0.5 ppm of gas alpha but a dangerously high level of 20 ppm of gas alpha existed around the plant, the detector would only transmit a signal telling the controller that an amount of gas alpha above 0.5 ppm had been detected. However, the actual concentration, i.e. the dangerously high 20 ppm of gas alpha, would not be relayed back to the control room. This type of system would not provide and quantitative documentation which may be useful in any number of situations.
Thus, a wireless gas monitoring system with heightened sensitivity is desirable. By this it is meant that it would be desirable to have monitors that monitor and relay more detailed information. The current invention does just that. The monitors will not only relay the actual amount of gas detected, i.e. 20 ppm, but they may also relay operating parameters of the system such as the battery voltage, day, date, time, wind speed, weather conditions, etc. existing at the time the gas was detected.
From the foregoing it is clear that certain improvements are desired. Many of the desired improvements have been accomplished by the current invention.
The present invention contemplates a new and improved method and apparatus for wireless gas monitoring which is simple in design, effective in use, and overcomes the foregoing difficulties and others while providing better and more advantageous overall results.